Collegiate Institute for Math and Science second-year Principal Shadia Alvarez stunned her hard-working kids last week by conveying the harsh ultimatum on a poster hung in the hallway near her office.

“Senior Prom 2013 CANCELLED Till further notice,” reads the color poster. “There will NOT be a PROM without a 100% Guarantee Graduation Rate.”

The poster, which is illustrated with images of dapper flappers and a steak-and-potatoes dinner plate, concludes by putting the onus on students: “Will there be a Senior Prom? How will you make this happen?”

But only seven schools in the whole city achieved a perfect graduation rate in 2012, according to preliminary city Department of Education figures — all of them schools that have entrance requirements.

“The prom is supposed to be like a reward for all the students who did well,” said one frustrated 18-year-old senior. “I think it’s unfair that the principal wants to punish everyone. It’s not our fault all those other kids failed.”

A source at the campus said the principal recently confirmed her intention to cancel the prom — unless all struggling seniors move mountains in the next three months — during a meeting with students.

“The seniors are being punished, [but] these kids are solid!” said the source. “It’s no way to motivate kids. If anything, she made it worse and ruined their dreams of a fun, memorable night with friends.”

Alvarez declined to speak with a reporter at the school and did not respond to an e-mail seeking comment.

A school staffer relayed a message from Alvarez — who was occupied with parent-teacher conferences — that said only, “I don’t know what poster you are talking about.”

A Department of Education spokeswoman said she didn’t know anything about the prom poster, either.

Not all kids took the threat as a serious one.

Justin Johnson, a 17-year-old senior, said he thought the poster was just a warning for students not to develop the common slackers’ syndrome known as “senioritis” — where kids coast through the last semester before graduation.

“I don’t think she really means it. It’s just a scare tactic to get the students to do better,” he said.

“But that’s not the right way to inspire us,” he added. “How about offering more after-school programs, more tutoring opportunities for Regents exams and finals. Why threaten us when you can help us?”